1. Field of the Invention
The present invention relates to a control device of an internal combustion engine in which a plurality of fuel injection valves are provided in each of a plurality of cylinders.
2. Description of the Related Art
Generally, in an internal combustion engine provided with an exhaust gas purification system utilizing a catalyst, it is essential to control a mixing ratio between air and fuel in an air-fuel mixture burned in the internal combustion engine, that is, an air-fuel ratio, in order to purify, with high efficiency, harmful components in the exhaust gas by the catalyst. In order to control the air-fuel ratio mentioned above, the internal combustion engine is provided with sensors that generate outputs in accordance with an amount of oxygen in the exhaust gas on the upstream and downstream sides of a catalyst, that is, a catalyst purifying device of an exhaust passage, and an air-fuel ratio feedback control is executed so as to cause the air-fuel ratio to follow a target air-fuel ratio on the basis of the outputs. For example, an air-fuel ratio control (a main feedback control) is executed on the basis of an output of a so-called wide-area air-fuel ratio sensor which is provided in the upstream side of the catalyst, while performing correction on the basis of an output of a so-called oxygen sensor which is provided in the downstream side of the catalyst (carrying out a sub feedback control).
Generally, in the internal combustion engine mentioned above, since the air-fuel ratio control is normally carried out by using the same control amount with respect to all the cylinders, an actual air-fuel ratio can vary between the cylinders even if executing the air-fuel ratio control. In the case where a degree of the variation is small, the variation can be absorbed by the air-fuel ratio feedback control, and the harmful components in the exhaust gas can be purified by the catalyst, and thus the emission is not affected, and any particular problem is not generated. However, in the case where the air-fuel ratio between the cylinders vary greatly, for example, due to failure in a fuel injection system or a valve system of an intake valve in a certain cylinder of the cylinders, the emission is deteriorated and a problem is generated. Furthermore, in the case where the air-fuel ratio between the cylinders vary greatly as mentioned above, the air-fuel ratio sensor on the upstream side of the catalyst has a strong tendency of producing the same output as that when the air-fuel ratio is richer than the theoretical air-fuel ratio, due to influence of hydrogen component in the exhaust gas, and the air-fuel ratio tends to shift to a lean side on the basis of the air-fuel ratio control. Therefore, it is desirable to suppress the shift to the lean side mentioned above.
For example, a fuel injection amount control device of an internal combustion engine described in International Publication No. WO2011/155073 is provided with a configuration of performing feedback correction of an amount of fuel to be injected by a fuel injection valve so that an air-fuel ratio expressed by an output value of an air-fuel ratio sensor on an upstream side of a catalyst coincides with a target air-fuel ratio which is set to a theoretical air-fuel ratio. Furthermore, the device is provided with a configuration of obtaining an index value which becomes larger in response to increase in a difference between the cylinders of the air-fuel ratio of the air-fuel mixture supplied to each of combustion chambers, and correcting so as to increase an amount of a fuel so that the air-fuel ratio comes to an air-fuel ratio which is richer than the theoretical air-fuel ratio in response to increase in the obtained index value.